Exemplary embodiments of the present disclosure relate to a gallium nitride (GaN)-based Schottky diode and a method of fabricating the same.
For rectification, a three-phase AC generator, a generator AC bridge, or a rectifier is used. In general, the rectifier is formed of 6 semiconductors each having a pn switching unit made of silicon. In order for the diodes to operate, the diodes are designed to tolerate high current (e.g., up to current density of 500 A/cm2) and high temperature (e.g., up to a depletion layer temperature Tj of <225° C.). In general, a voltage drop in a flow direction, that is, a flow voltage UF, is about 1 volt at high current levels. When the diodes operate in a blocking direction, a very low blocking current IR flows up to a breakdown voltage UZ. The blocking current greatly rises upon reaching the breakdown voltage UZ. Accordingly, rise of a voltage higher than the breakdown voltage UZ is suppressed.
Diodes are divided into a high-blocking diode (HS-diode) having a breakdown voltage UZ in a region between about 200 to 400 volts and a Z-diode having a blocking voltage in response to voltage of a vehicle electricity system between about 20 to 40 volts. The high-blocking diodes (HS-diodes) should not operate at breakdown. The Z-diodes may also be subject to a load up to a very high voltage within a short time at breakdown. Accordingly, the diodes are installed to restrict voltage of a generator that has excessively risen when a load varies or a load dump drops.
Some of the well-known disadvantages of a pn-diode flow voltage include a forward loss and reduced efficiency of the generator attributable to the forward loss. In a generator of 100 A, an average forward loss reaches about 200 W because two diodes connected in series are inserted into the center of the generator. The heating of diodes and a rectifier related to the generator needs to be reduced by expensive cooling measures (e.g., a cooler and/or a fan).
In general, so-called Schottky Barrier Diodes (SBDs) are mounted instead of the pn-diodes in order to reduce a forward loss. The Schottky-diode is a metal-semiconductor conversion device having an electrical characteristic curve similar to that of the pn-diode. Unlike in the pn-diode, in the Schottky-diode, a flow voltage can be freely selected within a specific limit by selecting a metal, and may be set to be lower than that of the pn-diode. Accordingly, the flow voltage UF of 0.5 V to 06 V, for example, may be implemented without difficulties. When metal is selected, a so-called (energy-) barrier height (PhiBn) is defined. Only electrons capable of overcoming the barrier may help a current flow. The barrier height may have an influence on properly selecting a “barrier metal”. Furthermore, the barrier height (PhiBn) is also applied to a semiconductor used (semiconductor materials: a covalent bond or ion semiconductor, n- or p-doping).
In general, the Schottky diode has low price competitiveness because it is made with an expensive gallium nitride (GaN) substrate.